While many investigators have looked at fragments of the developing phonological system in infants and young children, little work is available which provides an integrated view of phonological language acquisition. An investigation of the development of the perception and production of infants and young children during the first 30 months of life is proposed. The primarily longtudinal study will integrate the results of speech perception and speech production research from infants from two linguistic communities, Spanish and English, into a single framework. Emphasis will be placed on relationships between the developing perceptual system and the developing capacity to produce adult-like utterances. The primary methodologies for study of speech production will be specially modified transcription and categorization systems, as well as acoustic analysis. Methodologies for perception studies will be the VRISD (Visually Reinforced Infant Speech Discrimination) and Shell Game paradigms. This study will serve to: a. overcome ethnocentricity in theories of phonological development by evaluating the role of linguistic environment (Spanish or English on patterns of learning, b. elucidate the relationship between speech perception and speech production in phonological acquisition, c. specify the nature of stages of phonological development, starting at birth, and the relationships among these stages both in perception and production, d. broaden the data base concerning speech discrimination skills, e. demonstrate the development of speech perceptual capacities in infants, f. provide basic information concerning the learning of Spanish phonology by infants.